In recent, years, as a typical exhaust, gas purification device that is applied to a compression ignition-type internal combustion engine (hereinafter referred to as the “engine”), a device has been known that includes a NOx purification catalyst (hereinafter referred to as the “NSC”) and a catalyzed soot filter (hereinafter referred to as the “CSF”) on which a particulate combustion catalyst is supported. In this device, the NSC is provided in an exhaust passage immediately below the engine, and the CSF is provided in an exhaust passage on the downstream side of the NSC.
Here, the NSC oxidizes and purifies CO and HC contained in exhaust gas, captures NOx when the exhaust gas is lean, then enriches the captured NOx so as to perform desorption and reduces and purifies the exhaust gas to N2. The CSF captures particulates contained in the exhaust gas, and oxidizes and purifies the captured particulates with a particulate combustion catalyst.
As the particulate combustion catalyst described above, a particulate combustion catalyst is proposed in which an alloy formed with 75 to 25 mass % of Ag and 25 to 75 mass % of Pd is supported on an Al2O3 carrier (see, for example, Patent Document 1). It is thought that with the particulate combustion catalyst described above, regardless of the concentration of NOx in exhaust gas, it is possible to oxidize and purify particulates.
Patent Document 1: Japanese Patent No. 5524820